Construction is a game of uncertainties. Unforeseen circumstances pop up almost on a daily basis in a construction project. Being able to foresee them and to rectify the issues without a fatal effect defines the success of a project. Augmented reality helps in visualizing many of these unwanted errors which are hidden in the real world. This paper discusses the use of augmented reality in Planning and Execution stages of a construction project. The paper mainly focuses on the advantages of using augmented reality in the construction phases with emphasis on the methods adopted and the results obtained in various scenarios under consideration process. Further scope of the paper proposes increased use of augmented reality as a helpful tool for precise planning and higher productive efficiency in construction. KEYWORDS
Augmented reality, Construction Phases, Augmented reality in real world
Augmented reality is a live, direct, or indirect view of a physical, real-world environment whose elements are augmented by computer generated inputs. Augmented reality enhances a person’s perception about real-world. Augmented reality differs from Virtual reality in the basic concepts because the latter replaces the real world with a simulated, virtual world. Construction industry creations are based on the real world and if a better view of the entire project is obtained during the various phases, the efficiency and the results also will be better. Augmented reality can be used for aiding construction professionals in the various stages viz. Planning and Execution. During planning stage of construction there is a wide variety of hurdles to be crossed in which community development holds one of the key role. The beneficiaries and the neighborhood need to have a better understanding of the project and the various outcomes including impacts and prospects. During the planning stage of the project the professionals involved should have a clear idea of the direction of work and the various methods to be adopted for a smooth execution. Execution stage is the one of the most vulnerable stage in a construction process because of lack of vision of the workers. Augmented reality comes handy in the above mentioned scenarios.
1 Graduate Student, M.Eng, University of Michigan
2 Graduate Student, M.Eng, University of Michigan
3 Graduate Student, M.Eng, University of Michigan
4 Graduate Student, M.Eng, University of Michigan
5 Graduate Student, M.Eng, University of Michigan
This paper discusses impact of augmented reality in planning stage decision making scenario by the beneficiaries and neighborhood, an execution stage activity of discovering buried utility lines and a scenario of a complex staircase design. Detailed analysis on the use of augmented reality in each of the scenario with outcomes is illustrated in this paper. This paper flashes light into the future of augmented reality also with pivot on development and use in daily construction activities. PLANNING STAGE
Most of the construction projects face opposition before the actual construction process has started. When a new project is introduced, the neighbors are always concerned about the nuisance during the construction period, increase in traffic density, loss of open spaces, noise pollution, environmental problems caused harmful tools used on site. Likewise lot of problems are faced before the construction may even be started which might cause delays in the project. Time is an essential factor of any project. A survey of neighborhood reaction to a new development on Anderson Parkway in South Burlington showed the support and resistance before and after construction. The survey consisted of questions about how the project will have negative/positive impacts on traffic, space, property value, additional kids in neighborhood, crime or safety, etc.
The level of support before construction was at an average of 55%. This increased by 31% to a total of 72% support after construction. In the light of this survey and many more in the same regard, we can infer that if the people under concern had a clear idea of the project and could visualize the project on site, there will be less opposition from the neighbors and it will save valuable time.  Citing a case where augmented reality was used to aid the municipal decision makers have a better understanding of a project will substantiate this finding. Builders in Raseborg town of Southern Finland created an Augmented Reality model for outdoor visualization of their new hotel complex. They defined 3D model locations on maps for preparing the AR model. The existing buildings were shown transparent along with the solid planned ones. The viewing devices were either mobiles or laptops. Laptops had an advantage of higher functionality and a larger viewing screen. People were provided with mobile real time Augmented Reality visualizations along with traditional presentation methods. Decision makers could vie the plans from different locations according to their choice.
The project could be viewed from a distance also to know how it fits with the surrounding development. This gave a better understating of the entire project since all possible views were seen along with the naturally existing surroundings. Builders received very good feedback from the people: “Augmented Reality complemented traditional visualization methods well”, “Gives better impression of the building volume than other methods”, “Helps to understand the project being present there”.  Hence if Augmented Reality is implemented by builders to give a final perspective to the people in the neighborhood about the project, they will have a better understanding about the project, the worth of the project, and the benefits for the neighborhood. Projects could increase potential sales in the areas which would be largely appreciated by the local vendors, etc. Studies are also being conducted on how Augmented Reality can be used for showing traffic flow patterns. Thus Augmented Reality is a potential solution to convince the people and save time in getting the plans approved.  EXECUTION STAGE
Before a project embarks on its journey with excavation, the utility lines have to be located. Utility location is the process of identifying and labeling public utility mains which are buried underground in the project site. These mains may include lines for telephones, electricity distribution, natural gas, cable television, fiber optics, traffic lights, street lights, storm drains, water mains, and wastewater pipes. In some locations, major oil and gas pipelines, national defense communication lines, mass transit, rail and road tunnels also compete for space underground.  Necessity of locating underground utilities 
Above is a graph of the total number of damages to underground utilities reported in the state of Vermont. A total of 945 utility lines were damaged. Digging without knowing where the utility lines are marked is a potential hazard to the utilities. The present methods of marking the underground utilities are done on the ground with the help of paints, stakes or flags. In addition, if sufficient care is not exercised, a utility line may be overlooked or incorrectly marked in the marking process leading to the damage of the utility lines in the excavation process. The location of the utilities could be converted to CAD models which could be then augmented into the real world with the help of an augmented reality tool. With the help of augmented reality an operator of the excavator would exactly know the location of all the buried utilities and not hit them in the process. CAD Model Real Time View Augmented View
To further ease the job of the operator an automated visual/audio alert system is also developed. In the absence of such a system, the operator will have to constantly look at the display mounted inside the equipment. Also it becomes difficult for the operator to calculate the distance between the equipment end point and the subsurface lines, hence the system will constantly calculate this distance.If it is less than a particular threshold value, an alert message can be sounded to the operator. This would help the operator to concentrate in his task. Hence augmented reality could help preventing damage to utility lines and reduce the number of damages significantly.
Figure 1 Figure 2
During the execution stage AR supplemented by BIM has been successfully used on a real time basis on the site .In this case the architects Perkins and BNBuilders have made used of AR on the construction site in visualization of design, sequencing of trades and quality control of a set of architectural feature stairs in a laboratory tenant improvement for the Institute for Systems Biology, Seattle. 
The complex nature of the stairs was such that it required unorthodox sequencing of the steps and the welds which had to go in created a lot of confusion because of the preinstalled feature glass. To solve the above problems and to give an clear picture to the craftsmen and other engineers working in this project BNBuilders developed a 4D visualization and augmented reality tool incorporating vital information provided by the architect ,the structural steel, glass and railing dealers along with the models obtained from the subcontractors with their self-performed carpentry and layout information.
The Augmented reality tool which was developed had immediate results, it involved everyone in the project –the owner, the architect, the project engineers, the superintendents, the detailers, and the craft workers, who were easily able to grasp the design easily and instilled a sense of confidence in them to finish the work on time, where even the slightest installation errors could have cost them dearly without the AR tool. The building team handled the risk and could flawlessly execute the work using AR tool to get the most of the BIM data.
ADVANTAGES AND DISADVANTAGES OF AUGMENTED REALITY   
Over the years, to address the problem of under-utilization of BIM at the project site, the industry has been developing several tools and techniques to assist in bringing BIM data from the project trailer to project site. One of such tool is the “Augmented Reality” technology to overlay BIM onto the physical construction site. The benefits and limitations faced by the Augmented Reality system in the field of construction planning are described below
A major application area for the use of Augmented Reality in the field of construction is to provide Visual Aids for coordination of the entire process of construction. The usual process of coordination for the present condition of work areas involves verbal descriptions, notes or hand sketches to determine upcoming work flow or resource allocation. However such forms of communication can be easily misunderstood. In order to improve this situation AR can be utilized for construction simulation. Multiple still shots of an AR scene with 3D design super imposed on it in correct scale and location may allow the workers to understand the present condition of the work areas easily and would prevent them having the additional mental workload for simulating the paths of material, equipment by allowing the field staff/workers to see and rearrange the computer generated objects representing them inserted into the photo scene of the work area
Interpretation and communication:
Another key potential application for AR is to provide visual aids for interpreting drawings and specifications. Using AR, a selected portion of a 3D design model may be rendered spatially onto a field personnel’s view of the construction site in actual scale, location and orientation. This significantly reduces the mental work load for the field supervisor and can enable field staff to see a meaningful representation of a structure, equipment or component without having to always refer the specification documents on paper.
Limitations of AR:
Portability and outdoor use: Head–mounted Displays (HMD’s) which are necessary for AR are weighty and bulky and therefore restricts the usability and mobility of HMD for construction practice.
The issue with using Mobile devices for AR is it’s not suited for real time computing due to lack of graphic orientation and driver support and thereby obtaining poor video and image resolution. Lack of Motivation: Because of the technology development that is yet needed, there is lack of motivation for AR technology transfer.AR technology adoption is arguably a tremendous leap of technology and therefore might not be a truly cost-effective solution and its feasibility and profitability is not yet determined
Technological Limitations: Construction sites are expansive in nature and therefore the tracking system for AR in construction must be designed to cover a large range while maintaining fine accuracy. AR requires highly accurate trackers because even tiny tracker errors can cause noticeable misalignments (poor registration) between real and virtual objects. However no tracking systems have completely satisfied the unique demands of the construction field.
FUTURE OF AUGMENTED REALITY IN CONSTRUCTION INDUSTRY 
Augmented Reality has endless growth potentials in the emerging markets and has widespread applications everywhere. Augmented Reality tools help collaborate the various resources involved in a project from the owner, the architect, the contractors, the project engineer and the workers on site for a successful and on schedule completion of work. Leading construction firms are developing their own AR tools to improve the ease of use and its practical application on a construction project .They are also looking forward for people who develop BIM applications to integrate AR into their standard requirements.
For example the Vela Systems is developing a new augmented reality tool which enables the superintendents for simple field planning and design verifications using hand held tablets which has the plan and specification in them inputted into them and can easily be verified with the actual work on filed using the tablet’s camera which compares the real work on site with the electronic drawing and points out the error’s if any. Many other tools are in the development stages. Augmented Reality is still largely in the developmental stages in construction and the prototypes Augmented reality provides an equal platform for everyone to work collaboratively by giving access to vital information to everyone on and off site to avoid delays due to installation and other errors.
Augmented reality provides an equal platform for everyone to work collaboratively by giving access to vital information to everyone on and off site to avoid delays due to installation and other errors. systems are not yet fully functional to be adopted for widespread use on all project sites. The use of augmented reality and development potential is limitless once everyone including the common laborer is familiar with it and use it on daily basis .The Augmented Reality tool in the near future can successfully support the common field tasks such as follows: * Facilitating the operations, maintenance and commissioning of buildings. * Easy visualization of designs and other complex illustrations on site. * Layout and Installation
* Quality control and for inspection purposes.
* Location of concealed works.
* Helps in Clash Detection.
Although augmented reality is still a novel and relatively new technology it has enormous uncapped potential in the construction sector. This technology allows the user to see the real world augmented with additional information created by the computer and enhances the user perception and interaction with the real world.
This technology can achieve much high rates of sustainability and profitability in the construction sector. The development of Mobile augmented reality is crucial in the construction sector with respect to processing, visualization and positioning and therefore is progressively being introduced.
Amir H. Behzadan, and Vineet R. Kamat, Interactive Augmented Reality Visualization for Improved Damage Prevention and Maintenance of Underground Infrastructure
Source: Dace Campbell, AIA, LEED AP, BNBuilders
Survey of Neighborhood Reaction to New Affordable Housing Development http://www.vhfa.org/documents/neighbor-survey.pdf
 Mobile Visualization of new Hotel plan
Behzadan, A.H., and Kamat, V. R. (2008) Simulation and Visualization of Traffic Operations in Augmented Reality for Improved Planning and Design of Road Construction Projects http://phys.org/news/2012-04-augmented-reality-technology-tool-urban.html http://www.ijvr.org/issues/issue2-2010/paper1%20.pdf